1. Field of the Invention
The present invention relates to an image output apparatus, such as an image forming apparatus, which can output an image print product capable of accurately restoring embedded information therefrom.
2. Description of the Related Art
Enhancing the security in offices is now strongly required due to recent development of information technologies (IT). For example, according to recent cases, client information often leaks out of companies so easily that the protection of confidential information belonging to the company or privacy of individual persons becomes a big social problem.
To solve this problem, it is desired to introduce an appropriate Information Technology (IT) mechanism to a managing system for the confidential information. For example, setting an access authority to permit a user to access electronic confidential information or adding a monitoring apparatus to the firewall is effective to prevent the confidential information from leaking out of the company. It is also effective to inhibit bringing any portable medium (e.g., a notebook PC or a USB memory) into or out of the office.
If the confidential information is electronic data, the above-described IT mechanism can effectively function as a means for protecting the confidential information from leaking out of the system. This is because, when the confidential information is electronic data, the confidential information is only accessible via the IT mechanism. Thus, introducing the IT mechanism for the electronic confidential information is meaningful.
On the other hand, when the confidential information is printed on a paper or other recording medium by an image forming apparatus, the above-described conventional IT mechanism is no longer effective to protect the confidential information belonging to the company or the privacy of individual persons, although users may be asked to get a permission to bring the information out of the system. In this respect, compared to the electronic confidential information, ensuring the security of the confidential information printed on a recording medium is difficult.
To solve this problem, various information leak prevention methods are conventionally employed.
As an example method for preventing the leakage of the confidential information, the technique using an electronic watermark or a two-dimensional bar code can be used. More specifically, there is a system capable of embedding copy restriction information in document data, which can inhibit copying the confidential information on a paper or other recording medium. When an image forming apparatus performs a copy operation, the image forming apparatus restores the copy restriction information (i.e., detects copy allowance/inhibition information) to control execution/cancellation of the copy operation for each page.
The copy restriction information is not limited to simply allowing or inhibiting performing a copy operation. For example, as discussed in Japanese Patent Application Laid-Open No. 2003-280469, there is a system capable of embedding password information or user information (to be used to determine copy allowance) as conditional information to allow only specific users to copy the confidential information.
The above-described copy restriction information and trace information (i.e., information to be added to trace a user) can be collectively referred to as “additive security information” or “meta-information” in the following description.
To ensure the effect obtain by the above-described information leak prevention method, the additive security information needs to be accurately restored when the image forming apparatus performs a copy operation. In this respect, as discussed in Japanese Patent Application Laid-Open No. 2006-165889, there is a system capable of causing an image forming apparatus to read a print output product and correcting the additive security information to be added to a document based on the restored result.
Although the above-described system is configured to improve the accuracy in restoring the additive information by performing the correction on the restored result of the additive security information (meta-information), the correction may be ineffective for some types of documents. In this case, the additive security information cannot be restored even if the correction is performed. The reading operation of the additive security information cannot be accurately performed. Accordingly, the security system does not work as intended.